Many of us have been following the deadly tornado outbreak across 4 states on December 10-11, 2021, especially the town of Mayfield, KY which was decimated by a preliminary EF-4 rated tornado one mile wide with 190 mph winds.
In my storm chasing, part of my role and focus is on building sciences and the improvement of residential construction, specifically single-family homes, to help prevent or limit the loss of property and life. As a result, I have access to data and people with boots on the ground in that area who have been conducting damage surveys on behalf of the NWS.
In this blog post, I’d like to point out some things as they relate to what I also do as a home inspector to help you understand the importance of a properly built home and why we report on some things the way we do.
Nearly every Pre-Drywall Inspection we do has comments regarding the Anchor Bolts/Straps being improperly placed, unsecured, inadequate, etc. The comment goes on to say have the Anchor Strap Layout reviewed for proper spacing and design. The Design Engineer will specify the type of strapping, connection/fastener types, and placement in accordance with Code. This design and strapping is to secure the homes wall structure to the foundation, be it a slab or crawl space.
The straps are then placed, using a slab as an example, as the foundation is poured or just prior. As the concrete cures, the strapping is held in place by the concrete and then wrapped around the sill/base plate and secured. In most cases, the drawings are not used, the stud spacing is not considered, and the straps are placed near the ends and every 4-6 feet after. Sometimes the foundation consists of CMU blocks (cinder blocks) which are hollow and may or may not have concrete poured inside. Examples of different strap types are identified below.
The day prior to the tornado outbreak, strong winds pushed down the front range of the Rocky Mountains in Colorado. These winds were the result of the low-pressure system being ejected east and the pressure gradient between the two systems near one another created wind reports of greater than 100 mph in some areas. Numerous homes under construction received damage due to items improperly secured. None, perhaps, serve as a better example than this home which was improperly secured and missing straps. The winds rushed through the open framing lifting the home off the foundation.
In Mayfield, older homes faired far better. It’s a common misconception that new homes are just thrown up and lack quality. The truth is prior to code there were several things working in our favor that code simply cannot account for.
Are Older Homes Built Better?
Like with anything, it depends. But the fact that an old house has stood the test of time is usually a good sign. Older houses that used poor construction techniques and materials are often demolished and turned into something new. So the old homes that stick around often prove that they really don’t make them like they used to.
Better Materials
It’s not unusual for older homes to contain materials that would be way out of your price range today or maybe not available at all. Old growth wood is some of the strongest material to build a home out of. It comes from large trees that grew undisturbed, making their wood dense and heavy. Most old growth trees are endangered now so even if you have the cash it can be hard to get your hand on some. Add most older homes used plaster and lathe walls and you simply have a stronger structure.
Code is simply the “minimal” standards to which a hoe must be built. There were no minimum standards back in the day, and some of these old homes bear witness to the craftsmanship of these builders.
Granted these two homes don’t look like much now, however, the lowest level walls remained intact – providing some protection for the occupants and preventing total collapse or displacement of the home; thus, demonstrating the importance of how the home is secured to the foundation.
Now, let’s look at newer construction in Mayfield and see the difference and value found in proper securement of the home to the foundation and why it’s important these items are strictly adhered to and inspected when building a new home.
In both cases, the homes were lifted completely off the foundation and destroyed. Below is a closer examination of the anchor bolts. In both cases, the bolts were driven into a drilled portion of the CMU block and was secured only by tension as the bolt was screwed into the sheathing. This is in no way effective and provide little protection from straight line winds, much less an EF-4 tornado. This is how lives are lost and families changed forever.
There are builders locally who subscribe to this practice, and I’ve seen it passed by counties. It’s improper and not allowed by code. A few years ago, I had in depth discussions with a builder the county and a client on a home built in this manner north of Travelers Rest. The county inspector would not relent. The Builder would not repair. A meeting with the County at County Square and the former Code Department Director, when presented with thermal imaging detailing the problem, and a borescope photo of the issues agreed the connection was improper and the Builder was required to repair.
Damage caused by the bolts being ripped from the CMU block show just how quickly and easily this happens under severe weather conditions. Notice the mortar is nearly all but removed and seperated by the suction vortices as they lift the blocks.
Unrelated to homes, but demonstrative of the power of these beasts, the parking blocks secured into the ground by rebar have been moved or lifted off the rebar. Some on both ends rocked until the rebar released them. Note the varied bends in the rebar in different directions and consider the force applied by the vortices within the tornado that allowed the winds to squeeze underneath the blocks in the first place. Even the sometimes subtle things tell a story.
Never surprised by the damages found, nature has a way of humbling us to our core. Writing this as I prepare to head to MS/AL for a day of storm chasing tomorrow, and praying that as we continue to learn and study the weather, the collective lessons learned may help others.
Dave